Wheelchairs have been designed to provide transportation for the physically impaired, often emphasizing user comfort, portability and flexibility. Because of the individual needs and requirements of the wheelchair occupants, a variety of styles and shapes have been developed which cater to their specific needs. Thus, both manual and power driven wheelchair apparatus have become significantly more sophisticated during the past decade.
One advantageous feature common to both manual and power driven wheelchair apparatus is to design the wheelchair frame as lightweight and as compact as physically possible. Manual wheelchair frames, in particular, are often completely or partially foldable or collapsible which reduces the overall size of the wheelchair. Manual wheelchairs are thus particularly portable, storable and transportable in vehicles. Moreover, because of this collapsibility, special vehicle modifications are often not necessary to carry collapsible wheelchairs.
Power driven wheelchair apparatus, on the other hand, generally require a more rigid frame than their manual counterparts since the frame is ordinarily subjected to increased loads due to higher operating speeds. Further, the powered wheelchair frame must be strong enough to carry the weight of the batteries and electric motor assembly. Power driven wheelchair apparatus, accordingly, are usually bulkier and not as portable nor as collapsible as manual wheelchair apparatus.
To a limited extent, however, powered wheelchairs may be folded and/or collapsed. Often, the backrest portion of the seat support pivotally folds down from a generally vertical position to a generally horizontal position parallel to and atop the seat. This maneuver provides partial collapsibility of the wheelchair frame which reduces the overall dimensions. Typically, the backrest is locked in an operating vertical position by a pair of spring loaded latch pins which are positioned on opposing lateral sides at the back portion of the backrest. These pins are generally biased in an extended position to continuously engage corresponding receiving apertures provided in the seat support frame. The backrest, therefore, may be latched in the generally vertical position with respect to the seat support, and released for folding or pivoting to a position just above the seat.
One problem encountered with these spring loaded latch pin devices is that both latches must be simultaneously gripped and the latch pins disengaged in order to release the backrest from the deployed and latched position. Because the opposing latch pins are biased to an extended position to engage the receiving apertures, two-handed continuous manual engagement of the latches is generally necessary to withdraw both pins from both apertures. Furthermore, the backrest must be articulated simultaneously while holding the latch pins by an amount sufficient to move the latch pins out of alignment with the apertures.
Failure to continuously withdraw the pair of latch pins from the corresponding receiving apertures while simultaneously commencing movement of the backrest from the vertical position will permit the latch pins to pop back into the corresponding apertures. Two-handed manual operation of the latch pins, in addition, is particularly difficult for many physically impaired users. Often, the wheelchair occupant may have limited use of one or both hands. The occupant's safety may also be jeopardized since they may need one hand free for stability and leverage. Moreover, moving the backrest toward the horizontal position while gripping the backrest proximate latch pins area (i.e., to operate the latch pins) is not an optimum position to commence pivotal movement thereof. Accordingly, conventional wheelchair backrest latch assemblies can be very awkward and inconvenient for the physically impaired to use.
Another problem associated with the prior art backrest latch mechanisms is that even when the backrest is locked in the vertical position, the backrest is often unstable relative to the seat support assembly. In order to permit the physically impaired to withdraw the latch pin from the receiving aperture, the pin must be relatively loose and freely releasable when engaged with the aperture. Unfortunately, radial instability of the pin relative the receiving aperture causes the backrest to experience considerable angular movement relative to the seat support assembly. Such motion may be critical to those requiring upper torso stability while seated in the wheelchair.